# Destinations

> Official built-in destinations, maturity, requirements, and limitations.

- Canonical HTML: https://supabase.github.io/etl/reference/destinations/
- Agent-readable Markdown: https://supabase.github.io/etl/reference/destinations.md
- Source: https://github.com/supabase/etl/blob/main/site/content/docs/reference/destinations.mdx

Supabase ETL ships official destination implementations in the
`etl-destinations` crate. Enable only the destination feature you need when
embedding ETL or building the standalone replicator. **BigQuery is the stable,
recommended default.**

| Feature      | Destination     | Status      | Guidance                       |
| ------------ | --------------- | ----------- | ------------------------------ |
| `bigquery`   | Google BigQuery | Stable      | Recommended default            |
| `clickhouse` | ClickHouse      | In progress | Evaluate for your workload     |
| `ducklake`   | DuckLake        | In progress | Evaluate for your workload     |
| `snowflake`  | Snowflake       | In progress | Evaluate for your workload     |
| `iceberg`    | Apache Iceberg  | Deprecated  | Do not use for new deployments |

## Status definitions [#status-definitions]

* **Stable:** The most mature built-in destination and the recommended default.
  Review its limitations and validate it against your production workload.
* **In progress:** Functional, but behavior, configuration, schema support, and
  operational requirements may still change. Test recovery and schema changes
  before production use.
* **Deprecated:** Retained for compatibility but no longer recommended for new
  deployments. Plan to move away from it.

## BigQuery [#bigquery]

**Status: Stable**

BigQuery uses the BigQuery Storage Write API and BigQuery change data capture
to maintain destination tables. The standalone replicator guide uses BigQuery
as its default example.

### Limitations [#limitations]

* Every replicated source table needs a primary key, and all primary-key
  columns must be included in the publication.
* PostgreSQL arrays containing `NULL` elements are not supported.
* Supported schema changes are applied automatically, but PostgreSQL default
  expressions and backfill behavior are only supported where they map safely
  to BigQuery. See [Schema Changes](https://supabase.github.io/etl/explanation/schema-changes.md).

## ClickHouse [#clickhouse]

**Status: In progress**

ClickHouse supports a current-state layout with `ReplacingMergeTree` and an
append-only event-log layout with `MergeTree`.

### Limitations [#limitations-1]

* The default `ReplacingMergeTree` layout requires a source primary key with
  every primary-key column included in the publication, and requires
  ClickHouse 23.5 or newer.
* `MergeTree` preserves an append-only event log; it does not expose a
  current-state replica by itself.
* Tombstone cleanup and `OPTIMIZE ... FINAL CLEANUP` are operator-managed.

## DuckLake [#ducklake]

**Status: In progress**

DuckLake writes through DuckDB to a file or PostgreSQL catalog and local or
object storage.

### Limitations [#limitations-2]

* Data storage URLs currently support `file`, `s3`, and `gs` schemes.
* Deployments must account for the required DuckDB extensions and the catalog,
  storage, and maintenance services they configure.
* Primary-key sorting requires source tables to have a primary key; other
  sorting modes do not add that requirement.

## Snowflake [#snowflake]

**Status: In progress**

Snowflake uses direct Snowpipe Streaming and key-pair authentication.

### Limitations [#limitations-3]

* Setup requires a Snowflake user and role with the documented warehouse,
  database, and schema privileges.
* Schema evolution support is still in progress. Only defaults that ETL can
  translate safely are applied; unsupported expressions are skipped with a
  warning.
* Validate channel recovery, committed offsets, and account-specific resource
  limits before production use.

## Iceberg [#iceberg]

**Status: Deprecated**

The Apache Iceberg implementation is retained for compatibility and is not
recommended for new deployments.

### Limitations [#limitations-4]

* Schema-change DDL is not supported. A newer relation schema is rejected.
* The destination is deprecated and is not receiving the same product
  investment as the active destination implementations.

## Custom destinations and upstream support [#custom-destinations-and-upstream-support]

Adding an official destination is a long-term maintenance commitment. It
requires durable and idempotent writes, schema-evolution behavior, restart and
recovery coverage, integration infrastructure, credential handling, ongoing
dependency updates, and operational support. For that reason, maintainers are
careful about accepting new destination implementations upstream. Open an issue
or discussion before investing in an upstream implementation; acceptance is
not guaranteed.

You do not need to contribute a destination upstream to use ETL. Implement the
[`Destination`](https://supabase.github.io/etl/explanation/traits.md#destination) trait in your own Rust
project, wire it into `Pipeline::new`, and maintain it alongside your
application. See [Custom Implementations](https://supabase.github.io/etl/guides/custom-implementations.md) for
a complete example.